The present invention relates to a three part type propeller shaft for a vehicle such as an automobile, and more particularly relates to such a three part type propeller shaft which incorporates three Hooke type universal joints and one constant velocity type universal joint, and which is notable for smoothness and lack of wobbling and vibration.
As a propeller shaft assembly for a vehicle such as an automobile, it has long been conventional to employ a single part propeller shaft coupled at its front end by a first Hooke joint to the power output shaft of the transmission and at its rear end by a second Hooke joint to the power input shaft of the differential device of the vehicle. Further, it is known to utilize a two part propeller shaft assembly made up from two propeller shaft elements coupled together by a second Hooke joint, and as before coupled at its front end by a first Hooke joint to the power output shaft of the transmission and at its rear end by a third Hooke joint to the power input shaft of the differential device of the vehicle; this type of two part propeller shaft assembly was introduced in order to reduce the vibration and consequent noise level during high speed operation.
Further, recently there have been developed so called full time four wheel drive type vehicles, which are provided with a central differential apparatus for distributing power between the front wheels and the rear wheels of the vehicle. Such a central differential apparatus is typically provided with a selectably actuatable locking mechanism for selectably preventing it from providing differential action, at the will of the vehicle driver. Further, there are also known four wheel drive vehicles which can be selectably switched to two wheel drive operational mode or four wheel drive operational mode. Both these types of vehicles may typically include a transversely mounted engine whose crankshaft and rotational power axis extends transversely to the longitudinal axis of the body of the vehicle. In four wheel drive type vehicles with such a transversely mounted engine arrangement, the distance between the output side of the engine and transmission unit and the front end of the differential device for the rear wheels becomes even greater than heretofore, and accordingly the propeller shaft inevitably becomes longer. Accordingly, various types of three part propeller shaft assembly have begun to be utilized in such four wheel drive transverse engine type vehicle configurations. Such three part propeller shaft assemblies include three propeller shaft elements and four universal joints.
In more detail, such a three part propeller shaft assembly typically includes a first or front propeller shaft element rotationally coupled at its front end by a first universal joint to the rear end of the power output shaft of the engine, a second or center propeller shaft element rotationally coupled at its front end by a second universal joint to the rear end of said first propeller shaft element, and a third propeller shaft element rotationally coupled at its front end by a third universal joint to the rear end of said second propeller shaft element and rotationally coupled at its rear end by a fourth universal joint to the front end of the input shaft of the differential for the rear wheels of the vehicle. And the center propeller shaft element is typically rotatably and elastically mounted to the lower side of the floor of the vehicle body by two elastic center shaft bearing supports, one near each of its ends; this is done in order positively to support said center propeller shaft element and to limit the number of degrees of freedom of the propeller shaft assembly as a whole. With this kind of three part propeller shaft assembly, in order to maximize the space within the passenger compartment of the vehicle and so as to minimize the irregularity in the floor of the vehicle caused by the provision of the propeller shaft assembly passing thereunder from the front of the vehicle to the rear, it is known for the three propeller shaft elements and the four joints to be extended, not in a straight line, but with each joint bent through its own characteristic angle, and typically with the center propeller shaft element held lower than the other two propeller shaft elements. Also, in order to absorb the rotational fluctuations created at the Hooke joints, it is typical to dispose adjacent Hooke joints in opposite phases.
A problem that has occurred with such a system is as follows. In the above outlined construction, generally during the high speed operational condition the vibration level and the noise level are low, but upon occasion a new type of vibration noise phenomenon not seen in the case of vehicles provided with single part propeller shaft assemblies or vehicles provided with two part propeller shaft assemblies arises. This vibrational noise is considered to be caused by rotational fluctuations originating in the propeller shaft elements.
As is per se known, when a Hooke joint is bent through an angle and is transmitting load from one propeller shaft element to another, a force couple is created. Thus, wobbling and vibration are caused in the propeller shaft elements due to secondary force couples arising in the joint angles present between the three propeller shaft elements. In particular, when a full time four wheel drive vehicle including such a three part type propeller shaft assembly is operated with the central differential apparatus in the locked condition, or when a part time four wheel drive vehicle likewise incorporating such an assembly is operated in the four wheel drive condition, then the engine and the rear wheel differential device both move somewhat due to wheel torque set up due to the rotational difference between the front wheels and the rear wheels of the vehicle, and the rear end of the engine power output shaft and the front end of the power input shaft for the rear wheel differential device both tend to be pivoted upwards. The angles of the various joints of the three part type propeller shaft assembly are thereby increased, and the above explained problem of wobbling vibration and noise due to secondary force couples is accentuated.
One possible countermeasure for coping with this problem of wobbling vibration and noise due to secondary force couples would be to set the spring constants of the two elastic center shaft bearing supports for the center propeller shaft element to be greater, i.e. to make said center shaft bearing supports stiffer by, for example, using a stiffer rubber element in their constructions. Although this increasing of the spring constants of the two elastic center shaft bearing supports is effective for preventing or reducing such wobbling vibration and consequent noise, the general noise level as well as the booming noise level within the passenger compartment are undesirably increased, and this in practice makes such a solution not practicable. As a result, substantial reduction by this method of wobbling vibration and consequent noise is not possible. Furthermore, increasing the stiffness of the two elastic center shaft bearing supports has the further deleterious effect of reducing their durability.